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Home My WebLink About2014-03-05 PACKET 12.A.REQUEST OF CITY COUNCIL ACTION COUNCIL AGENDA MEETING ITEM # DATE 3/5/14 �� . PREPARED BY: Community Development Jennifer Levitt ORIGINATING DEPARTMENT STAFF AUTHOR *********�*****�****************�**�************ COUNCIL ACTION REQUEST: Workshop: Review and discuss changes to pavement specifications made by MnDOT over the years and changes to the 2014 Pavement Management prbject specifications. STAFF RECOMMENDATION: Workshop on pavement management. BUDGET IMPLICATION $N/A $N/AN N/A BUDGETED AMOUNT ACTUAL AMOUNT FUNDING SOURCE SUPPORTING DOCUMENTS � MEMO/LETTER: Memo from Ryan Burfeind dated 2/27/14 ❑ RESOLUTION: ❑ ORDINANCE: ❑ ENGINEERING RECOMMENDATION: ❑ LEGAL RECOMMENDATION: � OTHER: MnDOT Report Woodbury Presentation: pavement stripping in their community MnDOT Presentation: pavement specification history and new design considerations ADMINISTRATOR'S COMMENTS - �f� City Administrator ate ************************************************ COUNCIL ACTION TAKEN: ❑ APPROVED ❑ DENIED ❑ OTHER Cottage J Grove � Pride andPrOSPerity Meet To: From: Date: Re: Honorable Mayor and City Council Ryan Schroeder, City Administrator Ryan BurFeind, Graduate Engineer February 27, 2014 Bituminous Pavement Specification History 2014 Pavement Management Specification Changes Backqround Over the years, the Minnesota Department of Transportation has made several changes to the bituminous pavement specifications that are used when paving streets and highways through- out the State of Minnesota. The different specifications that are developed become the industry standard for paving throughout the state. There have been many changes from Specification 2331, which was used prior to 1988, to the current 2360 Specification known as Superpave. These changes cover a wide range of items from quality control and testing requirements to how a contractor is paid. Changes to the Pavement Management 2014 project. These include changes to i density testing and coring, topsoil, seeding Discussion specifications are also being made to improve the tems such as the bituminous pavement, pavement , and temporary erosion and sediment control. In the 2014 Pavement Management project, several areas are experiencing premature pave- ment failure due to stripping. This form of failure is not isolated to the City of Cottage Grove, but is occurring in communities throughout the state of Minnesota. Stripping is when the asphalt, or oil, in a bituminous pavement separates from the aggregate, weakening the pave- ment and allowing it to break apart. This is caused from moisture penetrating into the pavement, either from the surFace or below, which will then vaporize and separate the oil from the aggregate. Core samples that are taken in stripped pavements show a very porous struc- ture, where the oil has been blown out of the pavement. Stripping results in potholing of the pavement, with potholes increasing in size as the failure progresses. Changes to pavement specifications through the years can potentially be linked to this failure occurring, and subse- quently new specifications and testing requirements have been developed which have helped mitigate this issue. Prior to 1988, MnDOT Specification 2331 was used for bituminous paving. Under this specifi- cation the agency was responsible for the mix designs the contractor would use. There were also two separate pay items, one for the asphalt and another for producing and placing the mix. The agency was also responsible for quality control (QC) and acceptance. QC included checks on the asphalt and aggregate gradations. Contractors were responsible to produce and place the mix. The process of creating the bituminous mix was different than what is used to- day. It was mixed in a batch plant, so one individual batch of pavement was made at a time and then dumped into trucks. Today, continuous drum plants are more commonly used where Honorable Mayor, City Council, and Ryan Schroeder Bituminous Pavement Specification History 2014 Pavement Management Specification Modifications February 27, 2014 Page 2 of 6 materials are fed into a mixing drum at precise rates, heated, and then mixed with oil. The mix is then discharged into a hot store ready to be loaded into trucks. One major difference with the 2331 Specification and what is used today is how the pavement density was tested. Under 2331, the contractor would construct control strips where an em- ployee would follow behind the compaction equipment with a portable nuclear density gauge and take density readings. They would use this process to develop a rolling pattern that achieved the required densities. Once the rolling pattern was established, it would be used continuously until a new control strip would need to be constructed. Situations that would re- quire a new control strip included a change in the mix design or a change in the bituminous source. The Engineer was also able to request the construction of new control strips if more than ten days had passed without the construction of a control strip, or if they had other reasons to believe the required density was not being achieved. This is known as the ordinary compaction method. A majority of cities in Minnesota were still using the 2331 specification in 1998. In 1988, MnDOT came out with Specification 2340, which was labeled a quality management specification. The City of Cottage Grove adopted this specification in 1992. With this specifica- tion the contractor became involved in the mix design, and the asphalt and mixture were com- bined into one pay item. This was a major change, as contractors were no longer paid for the asphalt specifically, which is the most expensive part of a mix. Due to this change, it became desirable for contractors to reduce the amount of asphalt in the mix, resulting in "drier" mixes becoming more commonplace. One way to reduce the amount of asphalt was to reduce the amount of fine aggregate. In a bituminous mix, asphalt covers each aggregate particle, creat- ing what is known as the asphalt film. The greater the surFace area of the aggregate, the more asphalt is required to coat all of the particles. Reducing the amount of fines in the mix reduced the total surface area, which in turn reduced the amount of asphalt required. One major issue with reducing the fines and asphalt was it resulted in more voids in the in-place pavement. Ideally, the air content in a bituminous pavement will range between 3 to 7 percent. When the air content is greater than 7 percent, air voids can become interconnected. This created a more permeable pavement, which in turn allowed more water to penetrate the pavement and can lead to stripping. Under the 2340 Specification, the contractor started to be involved in QC testing. The agency was still responsible for acceptance, which was done through quality assurance (QA) testing. QA testing included tests on air voids, asphalt content, gradation, and density. As part of this specification, the procedures for density testing were changed. Rather than using a nuclear gauge to develop a rolling pattern, cores were taken of the in-place bituminous and tested. By taking these cores of the in-place pavement, the contractor was held accountable to ensure the pavement would meet the density requirements. This is known as the specified density method. In 1997, MnDOT made some changes to the 2340 Specification, coming out with the 2340 Modified Specification. The City of Cottage Grove adopted this specification in 1997 as well. The reason this specification was adopted immediately was MnDOT changed the grading system of the asphalt. They also increased the testing and frequency requirements. Addition- ally, two new mixture quality measures were added, voids in mineral aggregate (VMA) and Honorable Mayor, City Council, and Ryan Schroeder Bituminous Pavement Specification History 2014 Pavement Management Specification Modifications February 27, 2014 Page 3 of 6 tensile strength ratio (TSR). The VMA test determines the ratio of void space between aggre- gate particles in a compacted bituminous mix, which was the first attempt to address the "drier" mixes. This void space is comprised of the asphalt binder and air voids, which is important be- cause it relates to the strength, durability, and flexibility of a pavement. Not only will a drier pavement be more permeable, which can result in stripping, the pavement is also more brittle. In addition, too much asphalt binder between the aggregate particles will cause the strength of the pavement to be reduced and can result in increased rutting. Another cause of rutting is when the air void content in the pavement is below 3 percent. The reason for this is it will leave inadequate space for the asphalt to expand in hot weather, resulting in the pavement be- coming unstable. The TSR test is used to determine the moisture susceptibility of the pavement. This test de- termines the tensile strength ratio of a dry pavement sample compared to a saturated sample of the same pavement. The results of this test show how the strength of the pavement is affected by moisture. In 1998, MnDOT came out with two new specifications, the 2350 Specification (Marshall) and the 2360 Specification (Superpave). The 2350 Specification was designed for lower volume roads with traffic less than 3 million equivalent single axel load's (ESAL's). The City of Cottage Grove adopted this specification in 2002. In this specification MnDOT changed the mix desig- nations, increased density requirements, and included a ride quality component. They also added a Fines to Asphalt Ratio (F/A) test to go along with the VMA and TSR testing. The F/A test was important because a greater amount of fines would mean more asphalt, which would help address drier mixes. Finally, incentives and disincentives were added to this specification related to the density testing results. This was one of the reasons many municipalities delayed in adopting this specification, as they were not comfortable with paying the potential incentives. The reason for this was it created the inability to define the total project cost or maximum potential cost. The 2360 Specification was a companion to the 2350 Specification. It was originally designed for higher volume roads with ESAL's greater than 3 million and included some additional aggregate requirements. This specification included the same incentives/disincentives for pavement density as the 2350 Specification. One major difference between the 2350 and 2360 Specifications is how the bituminous pavement was compacted in the lab for testing. Under the 2350, a"puck" of pavement was pounded and then tested. For 2360, a form of gyratory com- paction is utilized, which is considered to most accurately replicate how pavement is compacted on a construction project. This will result in test results that are more representative of the pavement that is actually placed on a project. In 2003, MnDOT combined the 2350 and 2360 into a single standalone specification. The City of Cottage Grove adopted the specification in 2003 as well. Some additional aggregate re- quirements were added when combining the specifications. At this point MnDOT also began to push for 2360 to be used on all new construction. In 2010, MnDOT made the 2360 Specifica- tion the standard for all projects and traffic levels. They also added another testing require- ment, the Asphalt Film Thickness (AFT) test. This test shows how the aggregate is covered in asphalt and is a more informative test than VMA, which does not take into account gradations and compactions. Being able to see how the aggregate is covered in asphalt is key to ensuring Honorable Mayor, City Council, and Ryan Schroeder Bituminous Pavement Specification History 2014 Pavement Management Specification Modifications February 27, 2014 Page 4 of 6 a bituminous mixture is not to dry, and therefore less susceptible to moisture penetration. The City of Cottage Grove adopted 2360 in 2011. Changes to the pavement specifications over the past 25 years, including several new testing requirements and increased testing frequency, have resulted in the current 2360 Specification, which is believed to provide more durable pavement. In April 2013, MnDOT published a report regarding their findings from a study they had com- pleted on stripping in bituminous pavements that have been chip sealed. Their report indicated that stripping was a result of air voids being too great, allowing moisture to penetrate the pavement. However, they did not attribute the increased air voids to problems with the bitu- minous mixture, rather to problems with compaction. The report concludes that areas of the pavement are missed during the compaction process, so the required density is not achieved throughout the entire pavement. Questions have been raised regarding the conclusions stated in this report, resulting in MnDOT taking another look at pavement stripping. They are currently in the process of creating a task force that will further study the pavement stripping problem that is being seen in communities throughout the state. A copy of the report is included with this memo. Also included are presentations by Woodbury on pavement stripping in their com- munity and by MnDOT on pavement specification history and new design considerations. 2014 Pavement Manaqement Specification Chanqes Bituminous Pavement For the 2014 Pavement Management project, several modifications will be made to the specifi- cations to improve the overall project. The first changes to look at are MnDOT's most recent recommendations regarding pavement design specifications. The first is the use of '/-inch aggregate, instead of the 3 /-inch aggregate that is currently used. This will result in more sur- face area, more asphalt, and consequently a"tighter" mix with fewer voids. The potential cost impact is around $2 per ton of pavement. MnDOT's second recommendation is to specify 3 percent design air voids rather than 4 percent. This will increase the amount of asphalt in the mix, and once again create a"tighter" mix. The potential cost impacts are $1 per ton if "B" oil is used and $1.50 to $2 per ton if "C" oil is used. Oil, or asphalt, is graded from A to L, with each grade given different temperature ranges that it can tolerate. The temperature range gives a high temperature where rutting will be experienced, and a low temperature where cracking will be experienced. "C" oil is more resistive to cracking at lower temperatures, so it is more ex- pensive than "B" oil. The final recommendation that MnDOT has made is to increase the traffic level to 3 instead of 2. Traffic level 3 requires more crushed aggregate. This results in a more angular aggregate and more surFace area, which in increases the amount of asphalt. The potential cost impact for the higher traffic level is $1 per ton of pavement. All of these changes will result in more asphalt and a"tighter" mix, which will help reduce the pavement's suscepti- bility to stripping. The City also has some changes to the pavement specification, which we have used in the past. The first is to not allow reclaimed asphalt pavement (RAP) in the wear course of the pavement. This has cost an additional $7 per ton in the past, but is currently estimated at an additional $10 per ton. Another change is the requirement of "C" oil instead of "B", which would increase costs by $5 to $6 per ton. "C" oil is more costly than "B" and also limits the use of RAP to 20 percent, compared to "B" oil which allows for 30 percent. The overall potential cost Honorable Mayor, City Council, and Ryan Schroeder Bituminous Pavement Specification History 2014 Pavement Management Specification Modifications February 27, 2014 Page 5 of 6 impacts can be seen below, as compared to the 2013 Pavement Management prices. Note that "C" oil was used for 2013 Pavement Management project, so there is no additional cost for using it on the 2014 project. 2013 Pavement Management Non-Wear = $63/ton (with RAP) Wear = $70/ton (No RAP)) Potential Cost Impacts Non-Wear = $68/ton (with RAP) Wear = $78/ton (No RAP) si,soo,000 $1,600,000 � �- si,aoo,000 i si,ZOO,000 si,000,000 ssoo,000 � $600,000 " o 0 0 0 5aoo,000 � � szoo,000 /� � ,^„ S_ � t_�, __ Wear Course _ ..- _; -; _- —'°- -- o° ° _. �� o m , � M k N � _ � o o � � __ � � ` `^ �^ ° _�.; � rn --' °° �° — i� � ' -- L�_�_.; _ � r --- ---,— ' Non-Wear 7otal Cost Course ■ 2013 Specification ■ Modified Specification The final change regarding the bituminous pavement specification is in regards to the compac- tion method. For the 2014 Pavement Management project the ordinary compaction method will be used, where a nuclear density testing gauge will be used to create a rolling pattern that achieves the necessary density requirements. This eliminates the need to take core samples throughout the new pavement. Topsoil & Seeding Some other changes to the 2014 specifications are in regards to topsoil and seeding. Origi- nally, premium topsoil was going to be required on the 2014 project. However, as we are also going to have a%z-inch screening requirement, only select topsoil will be required. After the select topsoil is screened for material greater than a �/z-inch, the only difference would be some additional organic requirements for the premium topsoil. As the primary complaint with topsoil in the 2013 project was large rocks, the '/z-inch screen will achieve what we were looking for in the premium topsoil, without the additional cost. Also, with the new seeding process in the 2014 project, which is described below, the additional compost that will be placed with the seed will provide more organics. The City will be requiring sampling and testing of the to�soil that will be used on the project prior to the pre-construction meeting and that the sample is split and provided to the City for quality assurance testing. Also, the specification will be changed to state the contractor shall only remove as much soil behind the curb that is required to allow for proper compaction of new topsoil that is placed. The final change to the topsoil specification is the contractor will not be allowed to salvage any topsoil from on-site. In 2014 the Terraseeding process will be required. Terraseeding refers to a specific patented form of seeding where a 1-inch layer of compost, topsoil, and seed is blown in to provide a clean and finished look to the re-seeded areas. For this seeding process, the contractor will first place topsoil to fill the voids behind the curb. They will then come back and blow in the seed/compost mix. This mix can be tapered off as it meets the existing lawn surFace, providing Honorable Mayor, City Council, and Ryan Schroeder Bituminous Pavement Specification History 2014 Pavement Management Specification Modifications February 27, 2014 Page 6 of 6 for a very uniform finished grade. This compost and seed mix will also hold more water and provide more nutrients for the seed, increasing the germination rates. The seeding specifica- tion will also be changed to require re-seeding if germination is not seen in 14 days, rather than the 45 days that was allowed in the 2013 project. Additional Specification Changes There are several other modifications that will be made to the pavement management specifi- cation related to items such as utilities and trail construction. While not all of these changes directly affect the 2014 project, the changes will be in place for future projects. These addi- tional modifications include: 1. Allow star bond coating for water main fittings. 2. Add a grading tolerance to trail construction in an effort to prevent contractors from tolerancing the class 5 base with a skid loader. 3. Require gravel base density testing a maximum of 48 hours prior to paving, and require that the gravel base is free of frost prior to paving. 4. Change the temporary erosion and sediment control requirements to match state requirements, where maintenance is required when erosion and sediment control measures are at 50 percent capacity, rather than 30 percent. 5. Make the Platen lid the standard covers for sanitary and storm sewer castings. 6. Modify the bacteria testing requirements for water mains to state that if re-chlorination is required it shall follow Minnesota Department of Health and AW1NA guidelines. 7. Add requirements for keeping water main pipe clean prior to installation. 8. Require 100 percent crushed Class 5(limestone) for trail construction. 9. Do not allow recycled Class 7 in place of Class 5 aggregate for any supplemental gravel base that is placed for street construction. 10. Modify MnDOT's reduction in pay for failing aggregate gradations, clearly stating the reduction for aggregate backfill. Also modify the threshold between pay reduction and removal and replacement for failing gradation tests. 11.Include hydrant painting in the 2014 Pavement management project and prohibit the use of brush painting. 12.Allow precast thrust blocks to be used for water mains. 13. Make the R-3067-V and R-3067-VB castings the standard for storm sewer catch basins. The R-3067-V casting has a directional grate to be used on slopes, and the R-3067-VB has a bi-directional grate to be used at low points. Recommendation Review and discuss the changes to pavement specifications that have been made by MnDOT over the years and changes to the 2014 Pavement Management project specifications to ad- dress concerns raised in the 2013 Pavement Management project and at the Public Hearing. éÈÊÓÌÌÓÎÕÍÖôÍÈïÓÄûÉÌÔÛÐÈ ìÛÆ×Ï×ÎÈÉÇÎØ×ÊùÔÓÌé×ÛÐÉ èÔÍÏÛÉòåÍÍØìÊÓÏÛÊÃûÇÈÔÍÊ ïÓÎÎ×ÉÍÈÛø×ÌÛÊÈÏ×ÎÈÖÍèÊÛÎÉÌÍÊÈÛÈÓÍÎ ûÌÊÓÐ ê×É×ÛÊÙÔìÊÍÒ×ÙÈ öÓÎÛÐê×ÌÍÊÈ To request this document in an alternative format, please contact the Affirmative Action Office at 651-366-4723 or 1-800-657-3774 (Greater Minnesota); 711 or 1-800-627-3529 (Minnesota Relay). You may also send an e-mail to ADArequest.dot@state.mn.us. (Please request at least one week in advance). Technical Report Documentation Page 1. Report No.2.3. Recipients Accession No. MN/RC 2013-08 4. Title and Subtitle5. Report Date Stripping of Hot-Mix Asphalt Pavements under Chip SealsApril2013 6. 7. Author(s)8. Performing Organization Report No. Thomas J. Wood and Melissa K. Cole 9. Performing Organization Name and Address10. Project/Task/Work Unit No. Office of Materials and Road Research Minnesota Department of Transportation 11. Contract (C) or Grant (G) No. 395 John Ireland Boulevard, MS 330 (C)LAB904 St.Paul, MN 55155 12. Sponsoring Organization Name and Address13. Type of Report and Period Covered Minnesota Department of TransportationFinal Report Research Services 14. Sponsoring Agency Code 395 John Ireland Boulevard, MS 330 St. Paul, MN 55155 15. Supplementary Notes http://www.lrrb.org/pdf/201308.pdf 16. Abstract (Limit: 250 words) The higher costs of hot-mix asphalt pavement are causing more agencies to choose pavement preservation techniques to maintain their pavements. Some agencies have experienced stripping of the asphalt surface under chip seals, this distress appears to occur mostly in urban areas on curb and gutter streets. The main objective of the study was to determine what causes the stripping and to develop test methods to determine if the street will strip prior to placement of the chip seal. Both field and lab methods were used. Research focused on determining air voids, permeability, and density of the samples. Once these were determined, correlations were developed to determine the conclusions. 17. Document Analysis/Descriptors18. Availability Statement No restrictions. Document available from: Chip seals, Stripping (Pavements), Air voids, Density, National Technical Information Services, Pavements, Permeability, Preservation Alexandria, Virginia 22312 19. Security Class (this report)20. Security Class (this page)21. No. of Pages22. Price UnclassifiedUnclassified60 Stripping of Hot-Mix Asphalt Pavements under Chip Seals Final Report Prepared by: Thomas J. Wood Melissa K. Cole Office of Materials and Road Research Minnesota Department of Transportation April2013 Published by: Minnesota Department of Transportation Research Services 395 John Ireland Boulevard, MS 330 St. Paul, Minnesota 55155 This report documents the results of research conducted by the authors anddoes not necessarily represent the views or policies of the Minnesota Department of Transportation. This report does not contain a standard or specified technique. The authors andthe Minnesota Department of Transportationdo not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to this report. Acknowledgements Table of Contents Chapter 1.Introduction ............................................................................................................. 1 Chapter 2.Research Methodology ........................................................................................... 3 Chapter 3.Conclusions and Recommendations ...................................................................... 6 Appendix A: Task 1 Report Appendix B: Task 2 Report Appendix C: Task 3 Report Appendix D: Task 4 Report Appendix E: Task 5 Report List of Figures Executive Summary Stripping of hot-mix asphalt (HMA) under chip seals on urban streets has been an issuefor years. This project studied the issue to determine what causes the strippingand how to deal with the stripping. Low density or high air voids appear to be the main cause of the stripping. Lab testingvalidated the theory that HMA mixes not prone to stripping will strip if not properly compacted. Better construction methods are recommended. Chapter 1.Introduction Objectives of Research and Methodology This report represents task 6 –Draft Final Report of Local Road Research Board (LRRB) project number 904, Minnesota State Planning and Research project number MPR 10-(042)study entitled, “Stripping of Hot-Mix Asphalt Pavements under Chip Seals” . The objectives of this research project wereto determinewhysome streets suffer from stripping of the hot-mix asphalt (HMA)pavement afterplacement of asphalt chip seal.Using this data we will recommend how to determine if streets will suffer from strippingprior to chip sealing.Also recommendations will be made on how to improve performance of streets starting with pavingof the asphalt pavement. The research efforts where made up of the followingtasks: Task 1 Survey Cities and Counties to determine the extent of the stripping under chip seals. Task 2 Develop and modify existing test methods to determine is the HMA in place on streets is prone to stripping. Task 3 Coreand testthecores from City streets. Task 4 Reviewpast and presentconstruction methodsof citiesfor asphalt paving streets. Task 5 Analyzed thetest results from cores. Task 6 Draft final report Task 7 Final Report Task 8 Implementation Plan Background: Stripping Under Chip Seal Distress For more than twenty years, Cities have experienced pavement deterioration of the upper 0.5 to 1.0 inch of HMApavements under chip seals. The distress causing this is stripping of the asphalt layer directly beneath the chip seal (Figures 1 and 2). This distress starts as a small blister and becomes enlarged to the size of a small pothole; at which time the chip seal delaminates off of the asphalt pavement. With the high cost of asphalt, the use of pavement preservation treatments has grown rapidly as agencies preserve their roadway system. Most of the incidents of this distress have been located on urban curb and gutterstreets. If the distress is localized small patch will restore the street. However, as the area of deterioration expands a thin mill and overlay may be required to restore the street. This distress may lead to an expensive maintenance problem. 1 Figure 1:Stripping of asphalt pavement under chip seal. Figure 2:Asphalt deterioration under chip seal. Chapter 2.Research Methodology Task 1 Lowdensity may cause asphalt paving mixes to stripping to strip because of this low density and high air voids. Task 2 Task 3 Figure 3:Nuclear density tester. Task 4 Task 5 Task 6 and 7 Task 8 Chapter 3.Conclusions and Recommendations Conclusions Recommendations Appendix A: Task 1 Report Minnesota Local Road Research Board (LRRB) InvestigationNo.010-042 Stripping of Hot Mix Asphalt Pavements under Chip Seals Interim Report Submitted to the LRRB technical advisory panel in fulfillment of: Task 1 on November 9, 2010 Thomas J. Wood, Research Project Supervisor Mn/DOT Office of Materials and Road Research 1400 Gervais Avenue, Maplewood, Minnesota 55109 Introduction: In recent years, Mn/DOT has received reports of stripping, or deterioration, of the upper ½ to 1 inch of hot mixed asphalt (HMA) pavements under chip seal surface treatments. This distress (Figure 4) usually starts out as a small blister and develops to small potholes, at which point the chip seal delaminates from the pavement. These distresses can become an expensive maintenance problem. These distresses couldalso impede the deployment of cost saving preventive maintenance (PM) treatments if the treatments are viewed as the cause of the distresses. This reportrepresents task 1 of the Minnesota Local Road Research Board (LRRB) project number 2010-042, entitled, “Stripping of Hot Mixed Asphalt Pavements under Chip Seals”. The overall goal of this research project is to determine the underlying cause of the stripping distresses, identifying which pavements are at greatest risk and implement risk mitigation strategies that include improved specifications and practices. The main purpose of this task report was to identify the extent of the problem among local government entities. Minnesota cities and counties were asked to complete an online survey, using the TM Survey Monkey tool, describing their experience with the stripping under chip seal distress. Appendix A is a draft of the survey that was used to populate Survey Monkey™. The survey opened for response in early September and received 66 responses. Findings and Observations: The survey responses show that the problem of stripping of the HMA under a chip seal happens in over 60% of the agencies that responded. The first chip seals were applied when the streets were between four (4) and eight (8) years of age. The distress seems to appear between two (2) to four (4) years after chip seal application. Note that 60 percent of respondents reported that they did not have un-chip sealed roadways the same age as the chip sealed roadways. The ninth question asked for comments. Appendix A lists all the comments received. Below are a few selected comments. “As a rule of thumb, we will seal coat a street twice over a 15 to 20 year period prior to mill and overlay. Stripping more common after second seal coat.” “We have one road we sealed when it was only a year old and the stripping has not occurred on that road yet.” “So far this has only shown up in our first recycled asphalt wear courses installed from 1996 to 1998. We have heard that there was a problem with the Mn/DOT formula that hopefully has been corrected.” “We think this is occurring in pavements put down in the early 1990’s where they first started to use RAP in the mix.” Recommendations for next task: Based on the information from the survey, the research should to study the types of HMA mixes used to determine if some types, or blends, of HMA andrecycled asphalt pavement (RAP) are more prone to stripping. Density may also be a contributing factor. Appendix A: Survey Results asked the name of the Agency fill out survey Question 1: . Does your city use chip sealing as a Preventive Maintenance Question 2: treatment? 60 responded Yes, and 6 responded No. Ü±» §±«® ½·¬§ «» ½¸·° »¿´·²¹ ¿ ¿ Ð®»ª»²¬·ª» Ó¿·²¬»²¿²½» ¬®»¿¬³»²¬á ê Ç» Ò± êð Figure 2 Picture used in survey Using the pictures(Figure 2)aboveas guidance, do any of your Question 3: streets suffer from stripping under chip seals? 42 agencies reported yes and 24 reported No Ë·²¹ ¬¸» °·½¬«®» ¿¾±ª» ¿ ¹«·¼¿²½»ô ¼± ¿²§ ±º §±«® ¬®»»¬ «ºº»® º®±³ ¬®·°°·²¹ «²¼»® ½¸·° »¿´á îì Ç» Ò± ìî What percentage of streets does it happen on? Question 4: 40 out of 66 supplied answer to this question. See below histogram for breakdown of data. Most of the agencies reported a percentage but four(4) reported in format that did not give an answer easily converted to percentage. û ±º Í¬®»»¬ ©·¬¸ Í¬®·°°·²¹ ïì ïî ïî ïð é è ê ì Ú®»¯«»²½§ í ì î î î ï ï ï ï î ð ð ð ð ð ð ð Ð»®½»²¬¿¹» ±º Í¬®»»¬ ¬¸¿¬ «ºº»® ¬®·°°·²¹ . On average, what is the age of the street when the first chip seal is Question 5: placed? 52 responded to question see histogram for data below. Five (5) agencies reported in a different format which could not be captured by the histogram. ßª» ß¹» º±® º·®¬ ½¸·° »¿´ ïï ïî ç ïð è ë ë ê ì í í ì Ú®»¯«»²½§ î î î îï ð ð ð ð ð ð ð Ç»¿® ·²½» ½±²¬®«½¬·±² How long after the chip seal is placed does the stripping problem Question 6: show up? 52 responded to this question, see histogram below for data. Three (3) agencies reported in different format which could not be captured by the histogram. îë É¸¿¬ §»¿® ¼·¼ ¬®·° ¸±© «° îî îð ïë ïð ê Í»®·»ï ë ë ë í î ï ï ï ï ï ï ð ð ð ð ð ð Ç»¿® The responders that listed year zero have not seen any damage to their streets. Does your city have any streets that are the same age where some Question 7: have been chip sealed andsome have not? 52 responded. 21 replied yes and 31 replied no. Ü±» §±«® ½·¬§ ¸¿ª» ¿²§ ¬®»»¬ ¬¸¿¬ ¿®» ¬¸» ¿³» ¿¹» ©¸»®» ±³» ¸¿ª» ¾»»² ½¸·° »¿´»¼ ¿²¼ ±³» ¸¿ª» ²±¬á îï Ç» Ò± íï Does your city have complete construction records for street Question 8: construction that suffer from these distresses? 17 replied yes, 21 said no, and 14 replied with other answers. Ü±» §±«® ½·¬§ ¸¿ª» ½±³°´»¬» ½±²¬®«½¬·±² ®»½±®¼ º±® ¬®»»¬ ½±²¬®«½¬·±² ¬¸¿¬ «ºº»® º®±³ ¬¸»» ¼·¬®»»á ïì ïé Ç» Ò± Ñ¬¸»® ø°´»¿» °»½·º§÷ îï Are there any comments or additional information that you need or Question 9: would like to share? 16 responded with additional comments or information. See comments below. I'm going topass this on to my Public Works guys, as they have noticed this problem for several years. I will have them reply too, as they can offer more details. I would encourage everyone that this study include street maintenace personnel (field people) in addtion to City engineers/Public Works Directors (office people). As a rule of thumb, we will seal coat a street twice over a 15 to 20 year period prior to mill and overlay. Stripping more common after second seal coat. We have one road we sealed when it was only a year old and the stripping has not occured on that road yet You know all our comments about the chip seal material on sticking to our truck engines and tranny's... The City has been very consistent over the last 10 years or more about seal coatingand keeping up with the 5 year timing. To date we have not noticed any problems with the surface coat below the chip seal. We use MC oil and no emulsifiers which helps prevent this from happening. Our experience is limited to stripping on 61 wear course roads, we haven’t seen other significant stripping issues on other roads. We have attributed the problem more to the wear course being chip sealed then the chip seal itself Maplewood, like other metro cities is dealing with this issue and there are a number of state aid roadways with this problem. We are currently formulating an approach to fix these streets since it is very difficult to patch the great number of thin failures areas. According to our Street Superintendent the issue could be a result of using trap rock which is left for only 2-3 days before being swept up. Streets with pea rock left down for 2-3 weeks such as North Saint Paul and Lake Elmo don’t seem to be having the failures. We have not seen this problem in Faribault County. Marshall County has not completed a chip seal. So far this has only shown up in our first recycled asphalt wear courses installed from 1996 to 1998. We have heard that there was a problem with the Mn/DOT formula that hopefully has been corrected. In response to the question seven, we have not determined the ages for all occurrences of this type of stripping. We have however, noted that the stripping occurs in certain areas, where presumably the pavement is of approximately same age and sealing is also conducted at the same time (sealing is performed on an area basis). We seal streets on an 8-year cycle, and do not perform “early sealing” on new pavement after 2-3 years as some cities do. This program was initiated in the early 80s. We have started to examine the practice of early sealing, and would like to determine whether this would be more effective for our City. We think this is occurring in pavements put down in the early 1990’s where they first started to use RAP in the mix. Just a quick glance revealed two areas with most noticeable stripping were built around 1994- 1999 and mostly likely had two seal coat applications to date. Also these are areas of clay soils. Most problems appear where there are just thin overlays. One of the segments is approximately 15 years and the problem is pretty much continuous for the 10 mile segment. The problem is occurring in the center of lane and appears as a stripping problem created in the original mix placement. Possibly a segregation problem created by the paver during placement. Appendix B: Task 2 Report Stripping of Hot-Mix Asphalt Pavements under Chip Seals Development of a Methodology to Asses Potential at Risk Streets LRRB 10-0142,2010-042 Interim (Task 2)Report Mark J. Watson Thomas J. Wood April2011 Acknowledgements Table of Contents Chapter 1. Introduction................................................................................................................ 6 Objectives of Report and Research Stripping Under Chip Seal Distress Chapter 2. Laboratory Testing and Evaluation ......................................................................... 9 Introduction Laboratory Procedure and Test Results Chapter 3. Conclusions ............................................................................................................... 18 References .................................................................................................................................... 19 List of Figures before after List ofTables Executive Summary This report represents task 2 of the Minnesota Local Road Research Board (LRRB) proj ect number (Investigation) 2010-042, entitled, "Stripping of Hot Mixed Asphalt Pavements (HMA) under Chip Seals". The goal of this specific task report is to identify, or develop a methodology that can be used to asses potential at-risk streets before they are treated with a surface treatment. The preliminary methodology being investigated by the research team involves testing the in- place pavement for air void content, or permeability (either in-situ or laboratory). If the pavement is found to have excessive permeability and/or air void content, then caution should be exercised before placing a chip seal surface treatment; a fog seal surface treatment may be more appropriate. These recommendations are preliminary and need to be validated with more testing of laboratory and plant produced (in-place) pavement mixtures in accordance with the work plan. Based on previously completed forensic investigations, and survey responses the research team has hypothesized that low density (high-interconnected air voids) are a contributing factor to the observed stripping distresses. Thus, the experimental plan investigated the influence of various air void contents (7, 10 and 14%) on a mixture's susceptibility to moisture induced damage. The mixtures susceptibility was tested with: permeability tests, Mn/DOT modified Lottman, Asphalt Pavement Analyzer (APA) tested under wet and dry conditions, and a modified Iowa Boiling Test. Permeability testing indicated that the mixtures became significantly more permeable when the air void content was near 14%. The Lottman test did not show any visual evidence of stripping and all tensile strength ratios (TSR) were above 70%. However, the mixtures with the highest air void content had the lowest TSR at 74% and the mixture with the lowest air void content had the highest TSR at 84%. The change in air void content had the most dramatic influence on tensile strength values; a doubling of the air voids from 7% to 14% corresponded with a reduction of 52% and 58% in the dry and wet tensile strengths respectively. APA test results were mixed as the greatest difference in rutting rates between `wet' and `dry' testing conditions were at the 10% and 7% air void contents; the mixture with 14% air void content showed little difference. None of the mixtures showed signs of visual stripping. In the modified Iowa boiling test, the specimens with 14% air voids lost an average of 12.2% of their initial weight and the specimens with 7% air voids lost an average of 3.4% of their initial weight. In addition, empirical observations after the test showed that the specimen with the higher air voids (14%) was much less intact than the comparable specimens with lower air voids (7%). There was no test that explicitly showed asphalt stripping away from mixtures with higher air voids; however, the results of the laboratory testing did indicate that the higher voids do contribute to reduced pavement durability through reduced strength, increased susceptibility to rutting and increased permeability. The permeability and the modified Iowa Boiling test results indicate that pavements with higher air void contents may be more susceptible to moisture induced damage than pavements constructed with the proper amount. These factors will also reduce the life of a chip seal that's placed on top of a compromised pavement. Future testing within this proj ect will entail conducting the same tests (permeability, Mn/DOT modified Lottman, wet and dry APA, and modified Iowa Boiling) but on sealed specimens of varying density to more closely simulate field conditions. In addition, to the research team intends to modify the laboratory Permeameter to examine whether or not moisture (from the bottom) can penetrate a chip seal or a fog seal surface treatment. :� Chapter 1.Introduction Objectives of Report and Research Stripping Under Chip Seal Distress Review of Published Literature that stripping effects have been observed since the advent of paving with bituminous. Since this phenomenon has been detected, there have been numerous technical papers, articles, and presentations. Stripping is a complex problem to which there is no definitive, qualitative and quantitative solution towards understanding and predicting the stripping potential of HMA. There currently are a number of hypothesized mechanisms, including: detachment, displacement, spontaneous emulsification, film rupture, pore pressure, and hydraulic scouring. There are a number of postulated theories, which include: mechanical interlock, chemical reaction, molecular orientation, or Interracial phenomenon, none of which are universally accepted." Aschenbrener (3) reported on several pavements in Colorado which required complete rehabilitation at less than two years old and often less than one year old. The pavements designed to be a rut resistant composite pavement that used a plant mixed seal coat placed over an HNIA layer; however the underlying HNIA layer experienced severe moisture damage as shown below. Although the plant mixed seal coat was reported a contributing factor, the HMA mixtures were also deemed to be susceptible to moisture induced damage (the only reason to explain the rapid failures), and it was observed, through analysis of weather conditions, that the failures occurred during high levels of precipitation during the hottest part of the summer. The severe moisture damage did not correspond to freezing conditions. The failures were attributed to high temperatures, high moisture and high traffic. Kandhal and Rickards (3) was another reference that discussed the stripping problem in context of the pavement system and not in isolation. The researchers presented case histories of premature stripping of asphalt overlays due to stripping. The researchers observed that, "In each of the observed cases, saturation was the cause of the problem; stripping was the outcome." They also noted that, "If subsurface drainage of the pavement is inadequate, moisture and/or moisture vapor can move upwards due to capillary action and saturate the asphalt courses." The researchers hypothesized that, "In addition to high air void content, there are three essential ingredients to promote stripping: the presence of water, high stress and high temperature." Furthermore, the researchers argued that if the concept of mat "breathing" (ingress of moisture : Figure 1.2. A�ore showing Stripping below the surface (3) balanced by the egress of moisture in the form of water vapor) wasn't true, there would be substantially more stripping problems. The current investigation is concerned with stripping of generally older pavements with chip seals applied `late' (>7 years) in the pavement's service life. So, it is interesting to note that stripping almost universally occurs from the bottom up, or at the interface of two layers outward, so, based on this, it is logical to be concerned with the application of a chip seal over an HMA pavement, as the new pavement is now a"lower layer". In addition, section 7(surface treatments) of the Texas DOT Pavement Design Guide (5) recommends testing HMA mixtures for susceptibility to stripping before the application of a chip seal because, "A surface treatment will generally seal off the vertical escape of moisture migrating upward out of a pavement which can set up accelerated stripping in the existing HMA layer beneath the seal". The sealing off of the vertical escape of moisture will not increase the pavement's stripping susceptibility if there isn't moisture, in other words if the moisture can escape through the sides (edge drains), or if the moisture is intercepted with a permeable base layer. Thus this implies that the stripping mechanisms of the pavement were already in-place, merely accelerated by the presence of the chip seal surface treatment. Texas currently, as of 2011, has two standard methods for testing moisture susceptibility of HMA mixtures: 1. Placing a 200g sample of prepared HMA, no more than one aggregate thick in a beaker which is immersed in boiling oil 2. Modified Lottman Test which involves comparing the Tensile Strength Ration of moisture conditioned specimens with that of non-conditioned specimens. Aschenbrener and McGennis Q reported on using the boiling water test and seven versions of the modified Lottman test (AASHTO T 283) to predict the stripping of materials extracted from twenty sites of known field (stripping) performance. They reported that two levels of severity for conditioning laboratory samples correlated well with what was observed in the field; the most severe conditioning cycle included a 30-minute vacuum (610 mm HG) saturation a 15 hour freeze, followed by a 16 hour soak in a high temperature water bath, the milder conditioning consisted of: 55-80% saturation and no freeze, followed by a 16 hour soak in a high temperature water bath. They recommended the severe conditioning for mixtures placed under high traffic, high temperature, high moisture and possibly freeze conditions and milder laboratory conditioning for mixtures placed on low traffic sites. They went further, stating that it is critical that the conditioning in the laboratory (vacuum saturation, freeze, hot-water soak) be equal, or greater than the severity expected in the field. The authors did not recommend the boiling test as it is a very severe test that does not consider important factors of: gradation, void structure, or permeability, all of which influence field performance related to moisture susceptibility. .. Chapter 2.Laboratory Testing and Evaluation Introduction Laboratory Procedure and Test Results ã´² Ð»®³»¿¾·´·¬§ ªò Ü»²·¬§ íð îë îð ïë ïð ë ð éçòêïíòíÝÔò ë ß¹¹ Þ¿» ß·® Ê±·¼ô û 5�:r� 45C 4C�� c� � � ; �,r � � � ° .��:a�, � � � ZF�� * �' � ?i�ll� iii q} � �:SC � � ? �:��, �iu F�er�en# In-P��c� �4ir V�ids Figure 2.3. Permeability vs. In-Place Air Voids (Cooley Jr., Brown and Maghsoodloo, 2001). Lottman Test (Mn/DOT Modified� The moisture sensitivity was ascertained by performing modified Lottman tests in accordance with ASTM D 4867, Mn/DOT modified (See Appendix A). The moisture sensitivity was gauged by comparing splitting tensile test (Figure 2.4) results of control, or non-moisture conditioned specimens (dry strength) against those of moisture conditioned specimens (wet strength). The ratio of the wet strength to the dry strength represents the tensile strength ratio, or TSR. The generally accepted minimum threshold value for TSR is 70%. Figure 2.5 shows the TSR values vs. the air void content of the mix. All three TSR values are above the 70% criterion; however, the increase in air voids appears to correspond with a decrease in the TSR, which suggests reduced resistance to moisture induced damage. In addition, the apparent relationship appears to suggest that a mixture with 17% air voids, would have a TSR value of 70%. Figure 2.5 compares the visual appearance of the `wet' and `dry' specimens after testing. From this figure, there does not appear to be a relationship between air void content and stripping potential as all three sets appear to be relatively the same. B-11 U.� 1.1i 2.'..� ?�.'..� 4.'..� FJ.iJ FJ.LI ?.� 2.0 9.0 1'..l'..� i1.L� IL.L� ÌÍÎ ªò ß·® Ê±·¼ èêû § ã óïòëîìî¨ õ ðòçëì ÌÍÎ èìû În ã ðòççç Ð®»¼·½¬»¼ èîû èðû Ô·²»¿® øÌÍÎ÷ éèû Ô·²»¿® øÐ®»¼·½¬»¼÷ éêû éìû éîû éðû éûçûïïûïíûïëûïéû ß·® Ê±·¼ô û Ì»²·´» Í¬®»²¹¬¸ ªò ß·® Ê±·¼ ïîð ïðð Ü®§ Í¬®»²¹¬¸ É»¬ Í¬®»²¹¬¸ èð êð ìð îð ð éûèûçûïðûïïûïîûïíûïìû ß·® Ê±·¼ô û This test was performed under dry and wet (submerged) conditions. The wet APA was intended to simulate the three factors identified in the literature search as contributing to the stripping phenomenon: presence of water (saturation), high stress and high temperatures. Figure 2.9 and Figure 2.10 show the rut depth vs. the number of applied cycles for the wet and dry tests respectively. Table 2.1 shows the average rutting rate in mm per hour (mm/hr) for the three air void contents in the two different testing conditions (wet and dry). For consistency purposes the average rutting rate (measured rutting/number of cycles) was computed based upon the same number of cycles for both testing conditions, the test conditioned that governed the number of cycles appears as bold in the table. . , Figure 2.8. Asphalt Pavement Analyzer (APA), or Rut Tester Rut Depth 7%10%14% 14 12 10 8 6 4 2 0 Cycles (60 Cycles Per Minute) Avg. % Rutting RateDifference AVTestCycles(mm)(mm/hr) dry dry wet w�i��r�� r��r �w��.� r�� er;9�_��,�1��rM �vt��Pt� , �—_ . . ,� ,� ,� � � � � � � � � a �'�'� �'� �� a`� � �°,,� ��o- $�,�. ��,� ��,,� ��,��$ �� . ��, ,�� 1 ��,�. ^�,�� ry ��,� Cpcles (613 Cycfes Fer ki�inm.Ee� Figure 2.10. Asphalt Pavement Analyzer (APA) Test Results of Wet Test The mixtures with the higher air void contents rutted at a faster rate than those with smaller air void contents. The greatest difference in rutting rates between `wet' and `dry' testing conditions were at the 10% and 7% air void contents; the mixture with 14% air void content showed little difference. After testing in the wet condition the specimens were broken opened and examined for any visual evidence of stripping (Figure 2.11); there was no visual evidence of stripping among any of the test specimens, although there did appear to be some evidence of stripping where the hose interfaced with the mixture surface. : . Figure 2.11. Visual Examination of APA `wet' specimens before after Chapter 3.Conclusions References Stripping of Hot Mix Asphalt Pavements under Chip Seals: Task 1 Report: Survey of Local Entities, Unpublished . Stripping in HMA Mixtures: State-of-the-Art and Critical Review Of Test Methods Investigation of the Modified Lottman Test to Predict the Stripping Performance of Pavements in Colorado Premature Failure of Asphalt Overlays from Stripping: Case Histories Pavement Design Manual, Section 7: Surface Treatments Appendix C: Task 3 Report Chapter 2. Minnesota Department of Transportation Memo Chapter 3. Office of Materials TO:Tom Tesch DATE: July 17, 2012 SUBJECT:Task 3 memo for LRRB 904Stripping Under Chip Seal Study Stripping of Hot-Mix Asphalt Pavements under Chip Seals. Figure 14Nuclear Density Gauge Figure 15Coring at NI location ã´² Figure 16Lab Permeameter Figure 17Destroyed cores Figure 18Pavement in area of stripping Ü»²·¬§ ªò ß·® Ê±·¼ ¿²¼ Ð»®³»¿¾·´·¬§ ïîí îòë ïð î è ïòë êï ðòë ì ð î óðòë ðóï ïïðïîðïíðïìðïëðïêðïéð Ò«½´»¿® Ü»²·¬§ ø°½º÷ Figure 19Graph comparing Density vs. Air Voids & Permeability Appendix D: Task 4 Report Chapter 4. Minnesota Department of Transportation Memo Chapter 5. Office of Materials TO:Tom Tesch T.L. DATE: SUBJECT: Hot Mix Asphalt (HMA) MixturesHistory in Minnesota 2331 2340 2350/2360 2340 Mixes2360 Super Pave Crushing Volumetric Compaction Crushing: Air Voids Asphalt Film Thickness (AFT) TSR General Discussion . Recommendations Additional Needs for Research Appendix E: Task 5 Report Chapter 6. Minnesota Department of Transportation Memo Chapter 7. Office of Materials TO:Tom Tesch T.L. DATE: SUBJECT: Background Data ß·® Ê±·¼ ïîí ×²½¸ °»® Ü¿§ îòë Ô·²»¿® øß·® Ê±·¼÷ ïð Ô·²»¿® ø×²½¸ °»® Ü¿§÷ î è ïòë êï ðòë ì În ã ðòëéíê ð În ã ðòëèìê î óðòë óï ð ïïðïîðïíðïìðïëðïêðïéð Ò«½´»¿® Ü»²·¬§ ø´¾ñº¬í ÷ Figure 20 Air Voids and Permeability vs. Density èðð éðð În ã ðòêçîê êðð ëðð ìðð íðð îðð ïðð ð ðîìêèïðïîïìïêïè û ß·® Ê±·¼ Figure 21Air Voids vs. Lab Permeability Figure 22Permeability vs. In-Place Air Voids (Cooley Jr., Brown and Maghsoodloo, 2001). 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Implemented in 1988 Specification 2340 Density Pavement Aggregate Gradation Asphalt Content Air Voids Bituminous Mixture Criteria 2340 Acceptance (Assurance) Increased Testing and Frequency Susceptibility (TSR)Moisture Voids in Mineral Aggregate (VMA) New Mixture Quality Measures Enhancement to 2340 Implemented 1997 Specification 2340 Modified toward end resultMove Required on all MnDOT projects with --2360 (Superpave Gyratory design) MnDOT projects with traffic < 3 million on all Required --2350 (Marshall design) 2331 and 2340Replaced in 1998Implemented 2350/2360Specification Used on all Traffic Levels Superpave Gyratory Design Current Plant Mixed Asphalt Provision 2360Specification ( Agency/Industry ) grad., AV, AFT, crushing : Spotcheck, 2360 ( )Agency/Industry grad., AV, VMA, crushing Spotcheck, 2350/60: voids (, gradation, air 2340: Spotcheck Agency/Industry) )gradation (: Spotcheck, 2331 Agency testing rocess control testing.P Contractor Mix Design. Change from 2 bid items to 1 bid item. Over the Years Design/Production Changes Specified Density : Ordinary, Modified 2340 Maximum Density Strip, Specified Density : Ordinary, 2350/2360: Ordinary, Control 2331 2350/2360 2331/2340 Density Changes over the Years establish rolling pattern. Typically develop a control strip (growth curve) to No cores are cut. Ordinary Compaction Cores cut to determine density. .random basis Inspector determines and marks coring locations on a Maximum Density Method Compaction Methods Density Mixture Selection Aggregate Size 2360 Design Considerations percent passing the maximum aggregate sieve size. 100 containing RAP, if the oversize material originates from the RAP source. Ensure the virgin material meets the requirement of percent passing for mixtures The Contractor may reduce the gradation broadband for the maximum aggregate size to 97 * 8.0 3.0 7.0 2.0 7.0 2.0 7.0 2.0 mm] 200 [0.075 No. 80 45 60 25 65 25 70 45 mm] 8 [2.36 No. 95 65 75 30 80 30 90 60 mm] 4 [4.75 No. 100 90 35 100 85 mm] in [9.5 90 45 100 85 100* mm] in [12.5 ½ 100 85 100* mm] in [19.0 ¾ 100 mm] in [25.0 1 D C B A Sieve size Aggregate Gradation Broad Bands (percent passing of total washed gradation) 2-3139 Table Aggregate Size personal preference. Typically, aggregate selection is based on wear only-» Size. Minimum Lift Thickness: 2X Max. Aggregate Aggregate Considerations . Will make a better joint than coarser mixes» Less prone to segregation» Finer mixes are a little easier to compact» Similar to MV 4 mixes» lift final- Wearing Course Aggregate Size New construction or Overlay? Asphalt Binder Fast, Slow Traffic Type Traffic Levels Mixture Selection Bumping up of TL may be necessary for slow traffic. Select the Appropriate Traffic Level Mixture Based Aggregate quality levels are more restrictive. » Crushing, both coarse and fine, increases» Gyrations Increase» As Traffic Levels Increase: 5-Traffic Levels 2 Traffic Levels Adequate Void Properties Crushed Aggregate in both coarse and fine Rutting Pavements-Key to Non Aggregates in Hot Mix 28-or PG 64 28-PG 58» cracking happens. With overlay or mill and overlay construction it is Overlay (mill & overlay) 34-or PG 64 34-PG 58» will minimize potential for thermal cracking. With new or reconstruct, typically, select a grade that construct)-New (re Asphalt Binder Construction Type/Selection of 28). -28 instead of PG 58-(ex. PG 64 instead of 2) or specify higher asphalt binder grade Can either specify next higher Traffic Level (ex. 3 urban stop & go conditions. Average speeds slower than 45 mph, Slow No adjustments necessary mph, rural highways with sustained speeds. 45 speeds of greater than verage A --Fast Traffic Binder & Traffic Levelof Type/Selection Adjustments for Traffic SP Level 2: AADT < 2300 -Alternate: SPWEA230X ( -LVWE45030X ( -SPWEA240X ( -Alternate: SPWEB230X ( -LVWE35030X ( -SPWEB240X ( Gyratory (Superpave)Marshall (Example mixes shown) Mixture Designation Replacement Chart SP 3: 2300 < AADT < 6000 -Alternate: SPWEA330X ( -MVWE45035X ( -SPWEA340X ( -Alternate: SPWEB330X ( -MVWE35035X ( -SPWEB340X ( Gyratory (Superpave)Marshall (Example mixes shown) Mixture Designation Replacement Chart îèóø ÍÐÒÉÞîíðÞ ÷ ÐÙ ëè ÝÔßÍÍ ë ÒÑÒ ÉÛßÎ ÝÑËÎÍÛ Ó×ÈÌËÎÛ ÌÇÐÛ ÍÐ ïîòë íìóø ÍÐÉÛßîìðÝ ÷ ÐÙ ÈÈ ÉÛßÎ×ÒÙ ÝÑËÎÍÛ Ó×ÈÌËÎÛ ÌÇÐÛ ÍÐ ïîòë Ô×ÚÌÍ÷ [Note: Thicknesses Dependent on Foundation] New Construction Example Typical Section for Mainline Pavement mixture performance.to virgin equivalent MnDOT has seen RAP mixture performance RAP has economical & environmental value. 28-with PG XXratio of 70% AC add/total Meet 34-PG XXwith % Meet add/total AC ratio of 80 specification:permissively by Allowed RAP Following the correct procedures and paying attention to details » Using the best construction techniques.» the joints. Ensuring we get adequate density or compaction on the roadway and at » of mixture as it is being placed. Proper placement, including uniform tack coat application and no segregation » :We also need to pay attention to performance on the roadway. minimum. Keep number of mixes specified on a project to a .adequate for meeting given traffic levels and conditions Select an aggregate and asphalt binder combination Intelligent Compaction Paver Mounted Temperature Bar New Technology reading interval = every 6 inches 12 sensors spaced 1 foot apart, Temperature Bar Paver Mounted Infrared Quality Management Special Provision 2016 GPS coordinates Paver Stops and duration Paver Speed foot segments) Measure temperature differentials (150 Paver Mounted Infrared Temperature Bar Intelligent Compaction Smoother rides. FHWA Improved life cycle cost. Extended service life. Better asphalt pavements. Final Payoff Questions? Thank You